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United States Patent 3,059,532 OPTICAL SYSTEM Thomas I. Harris,Mundelein, and Irving C. Sandback,

Morton Grove, Ill., assignors to Bell & Howell Company, Chicago, Ill., acorporation of Illinois Filed Jan. 12, 1959, Ser. No. 786,276 2 Claims.(Cl. 88-57) This invention relates to an optical system, and moreparticularly to a highly corrected afocal telephoto attachment for usewith a prime lens of a camera.

An object of the invention is to provide a telephoto objective in whichthe positive power is divided between a plurality of components toprovide high corrections of both axial and lateral color.

Another object of the invention is to provide a highly correctedtelephoto attachment which is very compact.

Still another object of the invention is to provide an opticalattachment having a rear component which is very thick so that the sizeof the attachment is minimized.

A further object of the invention is to provide a telephoto attachmentvery compact in size and highly cor rected for both third and higherorder optical aberrations. The attachment may include a positivemulticomponent front member and a negative rear member.

It is to be understood'that the terms front and rear as herein usedrefer to the ends of the objective respectively nearer the longer andshorter conjugates thereof.

In the accompanying drawings:

FIG. 1 is a longitudinal section of an objective forming a specificembodiment of the invention; and

FIG. 2 is a longitudinal section of an objective forming a modificationof the objective shown in FIG. 1.

The invention provides a lens system which may be in the form of atelephoto attachment in which the axial thicknesses of the glasscomprise at least sixty-five percent of the overall length of thesystem. The attachment has a front positive group of components at leastone of which is compounded and a thick negative rear component, and ishighly corrected for both axial and lateral color aberrations as Well asthe other optical aberrations.

Referring to FIG. 1 of the drawings, there is shown an o tical objectiveincluding components 1, 2 and 3 forming ian afocal telephoto attachment4 for use with a prime lens o a camera; The components 1, 2 and 3include lenses L to 6 aving radii of curvature of their optical surfacesR to R axial thicknesses I to I and axial separations s and s Thecomponent 1 is a cemented biconvex tripiet, the component 2 a simplepositive meniscus concave to the rear and the component 3 a biconcavecemented doublet. The component 2 also may be compounded to increasechromatic correction.

The components 1 and 2 are positive and constitute a positive group ormember which is highly corrected for color both axial and lateral andthe component 3 is a negative member. For compactness of the attachment,the axial thickness of the component 3 should be at least twenty percentof the overall axial length of the attachment. Also, to obtain a highdegree of correction of higher order spherical aberration, coma andastigmatism as well as to correct other optical aberrations, the attachment should comply substantially with the following algebraicinequalities:

where, of the three components, F and R designate, respectively, thefirst, and last surfaces of component 1, F and R, the first and lastsurfaces of the second component, 1 and R the first and last surfaces ofthe rear component, f the focal length of component 1, f the combinedfocal length of the components 1 and 2 and A the focal length of thecomponent 3.

To keep the aberrations at a minimum, the attachment also should complywith the following algebraic inequality:

where R' R' and F' are algebraic numbers corresponding to the numbers ofinches of R R and F Superior correction for distortion and reduced sizeis achieved through the use of high index glass and thick elements inthe attachment shown in FIG. 1 and its magnification is 2.058. Thecomponent 1 is made up of three elements principally to achieve superiorcorrection of both axial and lateral color. To achieve compactness, thecombined thicknesses of the components must be at least sixtyfivepercent of the length of the unit, the thickness of the rear component 3should be at least twenty percent of the overall length of theattachment.

A preferred example of the attachment shown in FIG. 1 is constructed incompliance with the following example in which dimensions are in termsof inches, n designates the indices of refraction for the sodium D lineand V the Abbe dispersion numbers:

Ri=+1.950 L1 t1=.457 'na=1.697 V=56.2

t2=.120 na=1.720 V=29.3 Ra=+2.737

t =.350 na=l.697 V=56.2 R4=6.326

a1=.060 R5=+2.0689 L4 !4=.200 na=1.697 V=56.2

81=.075 R1=3.550 Ls t =.283 m=1.720 V=29.3

Rs=1.000 L0 ts=.450 na=1.697 V=56.2

A modified form of the invention shown in FIG. 2

includes a telephoto attachment 14 for use with a prime lens 15. Theattachment includes a front positive mem her or group of lenses composedof two positive components 11 and 12, and also has a rear negativecomponent 13. The components 11, 12 and 13 include lenses L to L havingradii of curvature R to R19, axial thicknesses t to I and axialseparations s and s and the attachment is spaced axial separations sfrom the prime lens. For compactness, the component 13 is greater inaxial thickness than twenty percent of the overall axial length of theattachment and the sum of t to is greater than sixty-five percent of theoverall length of the attachment. To provide a very high degree ofcorrection, the attachment is constructed in compliance with thealgebraic inequalities listed above in connection with the descriptionof the attachment 4 shown in FIG. 1.

A preferred example of the attachment 14 is constructed in compliancewith the following table in which dimensions are in terms of inches andn designates the refractive indices for the sodium D line, V the Abbedispersion numbers and f 13 4, and i the equivalent focal lengths of thecomponent 11, the components 11 and 12 and the component 13,respectively:

While the above objectives have been described as combinations of primelenses and 15 and attachments 4 and 14 detachable from the prime lenses,the attachments obviously may be made permanent with the prime lenses inwhich constructions, the attachments may bepf the focal type rather thanafocal"with cornpensating changes in the prime le'iises. Also, while thecomponents 1, 3, 11,12 and 131m: in the form of cemented compoundcomponents, they obviously may be of the air separated or edge contacttype. Further, the components 3 and 13 while shown as compoundcomponents may be simple negative lenses.

The attachments 4 and 14 are highly corrected, compact afocal lenssystems, and effect high magnifications.

being further characterized in that the system is'constructed insubstantial compliance with the following table in which dimensions arein terms of inches, and proceeding from front to rear, L to L designatethe lenses, R to R the respective radii of curvature of the surfaces, tto t the axial thicknesses, s and s the axial separations, n the indicesof refraction for the sodium D line and V the Abbe dispersion numbers:

2. In a telephoto lens system, a front positive cemented doublet, anintermediate positive meniscus cemented doublet, and a rear biconcavecemented doublet, and being further characterizedin that said system isconstructed in substantial compliance with the following table in whichdimensions are in terms of inches, and proceeding from front to rear Lto L designate the lenses, R to R the radii of curvature of thesurfaces, t to t the axial thicknesses, S and s the axial separations, nthe indices of refraction for the sodium D line and V the Abbedispersion numbers:

Ru=+1.867 L i11=.600 na=l.517 V=64.E

R11=2.400 L" m=.120 114:1.720 V=29.3

81 =.1642 R1t=+2.258 L1: t1s=.283 1ta=1.620 V=60.0 L RFJMO hr n 1 s49v-a3 s 81g=.405 R11=-2.125 L" m=.400 m=1.720 v=29.a

Rip-.707 L1, m=.275 na=1.697 V=56.2

R q=+1.23l

References Cited in the file of this patent UNITED STATES PATENTS2,169,130 Tronnier et al Aug. 8, 1939 2,184,018 Ort Dec. 19, 19392,366,597 Cox Jan. 2, 1945 2,387,497 Cox Oct. 23, 1945 2,394,635 ReissFeb. 12, 1946 2,433,438 Cox Dec. 30, 1947 2,803,167 Kohler et a1 Aug.20, 1957 2,913,956 Solisch Nov. 24, 1959

